1. Field of the Invention
This invention relates to an improved functionally gradated hydrostatic bearing and a bearing assembly. It is particularly directed to an improvement in the composition of the bearing assembly accomplished by the use of a gradated matrix composite forming the bearing.
2. Background Art
The function of a hydrostatic bearing is to provide centering and/or axial position control of a rotating member with a hydrostatic fluid film. The hydrostatic fluid film prevents metal to metal contact between the rotating shaft and the stationary bearing, thereby providing unlimited operating life. There is, however, metal to metal relative motion during start and shut-down transients when the hydrostatic film is not developed.
Another requirement of the hydrostatic bearing is to have very small predictable operating clearances between the rotating shaft and stationary bearing. To satisfy both of these requirements, a material must be selected that is wear resistant, has a low coefficient of friction when contacting the rotating shaft, and is thermally compatible with the shaft material.
Various bearing assembly configurations are disclosed, such as for example, in the following documents incorporated by reference.
U.S. Pat. No. 4,075,364 of Feb. 21, 1978 describes porous ceramic seals capable of withstanding extreme differences in amounts of thermal expansion during, for example, turbine operation.
U.S. Pat. No. 4,293,171 of Oct. 6, 1981 describes an anti-friction bearing wherein at least one rolling element is coated with an intermediate metal layer such as by ion plating, said metal layer having lubricating properties.
However, it is heretofore unknown to provide, in a bearing assembly, a bearing which possesses inherent anti-friction properties and high wear resistance.